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Article DOI: https://doi.org/10.3201/eid2910.230055
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Emergence of SARS-CoV-2 Delta Variant
and Effect of Nonpharmaceutical
Interventions, British Columbia, Canada
Appendix
Appendix Figure 1. Seven-day rolling COVID-19 incidence rate per 100,000 people and select non-
pharmaceutical interventions in place in British Columbia, Canada and England, March 1 to June 30,
2021. See Appendix Table 1 for more information on changes in public health and social measures, or
non-pharmaceutical interventions, implemented per jurisdiction over the study period. Data for 7-day
rolling COVID-19 incidence rate for England extracted from UK Health Security Agency COVID-19
dashboard (1). BC, British Columbia; VOC, variant of concern.
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Appendix Table 1. Timeline of nonpharmaceutical interventions in place in British Columbia, Canada and England, March 1 to June
30, 2021
British Columbia (BC)
England
Time period: March 1 to March 29, 2021
Time period: March 1 to March 7, 2021
Continuation of mandatory public health orders first
implemented in BC on November 19, 2020 (2–4):
Continuation of England’s third national lockdown first
implemented on January 6, 2021 (5):
• Physical distancing and masks required in public indoor
settings
• Stay-at-home order other than for essential reasons, including
essential medical needs, food shopping, exercise, and work if
cannot be done from home
• All school staff and middle and secondary school students
required to wear non-medical masks indoors (other than when at
their desks or workstations)
• Outdoor exercise can be done with your household or bubble,
or with 1 person from another household
Personal gatherings:
• All schools, colleges, and universities generally closed or
switched to remote learning, with some exceptions (e.g.,
university students taking hands-on subjects such as medicine)
• No indoor gatherings with people outside immediate
household or core bubble (maximum of two people outside
household)
• Early years settings (e.g., nurseries) remain open
• Starting March 11: outdoor gatherings with people outside
household or core bubble of up to 10 people allowed (6)
• Indoor worship services continue, with social distancing
Organized gatherings:
• Recreational facilities and outdoor sports venues closed
• All indoor and outdoor events are prohibited, with the
exception of baptisms, funerals, and weddings with up to 10
people including an officiant*; no associated receptions in any
venue
• Amateur team sports not allowed
• Indoor worship services suspended; limited outdoor worship
services allowed
• Restaurants only offering takeaway meals or food delivery; no
indoor dining
Travel:
Time period: March 8 to March 28, 2021
• All non-essential travel outside of one’s community strongly
discouraged
Step 1A of UK’s Roadmap out of lockdown begins (7):
Businesses, offices, and workplaces:
• Primary and secondary schools and colleges reopen with
outdoor after-school sports and activities allowed
• Indoor and outdoor dining allowed with own household or core
bubble, up to 6 people per table
o Secondary school and college students and staff required to
wear face masks indoors, with voluntary twice-weekly at-home
COVID-19 testing
• All businesses and workplaces must conduct active daily
screening of all workers using their COVID-19 Safety Plans, and
masks must be worn in common areas
o Primary school staff expected to wear face masks in corridors
and communal areas where social distancing between adults
not possible
• Offices should support work-from-home options wherever
possible
• University students on practical courses may also return to in-
person learning
Sports and exercise:
Time period: March 29 to April 11, 2021
• Indoor group low intensity exercise (e.g., Pilates, hatha yoga)
allowed
Step 1B of Roadmap (8):
• Indoor group high intensity exercise (e.g., dance, spin, power
yoga, circuit training) not permitted
Personal gatherings:
• Indoor and outdoor team sports not permitted
• Outdoor gatherings of up to 6 people or 2 households allowed
Time period: March 30 to April 22, 2021
Travel:
Circuit breaker starts (initially March 30-April 19) (9):
• Stay-at-home order replaced with recommendation to “stay
local”
• All school staff and students down to Grade 4 now required to
wear masks while indoors at school (including at their desks)
and on school buses; masks strongly encouraged for students in
kindergarten to grade 3
Sports and exercise:
Personal gatherings:
• Outdoor sports facilities reopen
• Indoor gatherings continue to be restricted
• Amateur organized team sports allowed, and not subject to the
limits on gatherings
• Outdoor gatherings of up to 10 people continue to be allowed
Time period: April 12 to May 16, 2021
Organized gatherings:
Step 2 of Roadmap (10):
• Indoor worship services suspended. Outdoor worship services
may continue.
Businesses:
Travel:
• Non-essential retail and personal care open
• Travel within province limited to essential travel only (e.g., work
or medical purposes)
• Public buildings (e.g., libraries, community centers) open
• Whistler-Blackcomb ski resort closed, to address and prevent
community spread related to non-essential travel
• Self-contained holiday accommodation open
Businesses:
• Outdoor hospitality open
• Indoor dining suspended
• Outdoor attractions and settings open
• Patios remain open, for dining with immediate household or
core bubble only
Sports and exercise:
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British Columbia (BC)
England
Offices and workplaces:
• Indoor leisure facilities (e.g., gyms, swimming pools) open for
individuals or within-household groups
• All workers strongly encouraged to work from home, where
possible
• All indoor children’s activities, including sport, resume
Sports and exercise:
• Indoor parent and child groups of up to 15 people (not
including children <5 y) resume
• Indoor, adult group fitness activities suspended
Time period: May 17 to June 30, 2021
• Gyms and fitness centers restricted to individual or one-on-one
activities
Step 3 of Roadmap (11):
Time period: April 23 to May 24, 2021
• Face coverings no longer required in schools
Circuit breaker extended on April 19, with additional travel
restrictions implemented April 23 (12):
Personal gatherings:
• Continuation of circuit breaker measures put in place on March
30, 2021
• Indoor gatherings allowed for up to 6 people or 2 households
• Additional travel restriction enforcement within province to
further discourage non-essential travel
• Outdoor gatherings allowed for up to 30 people
The Government of Canada implemented a travel ban on direct
flights from India and Pakistan beginning the evening of April 22,
2021.
Organized gatherings:
Time period: May 25 to June 14, 2021
• Outdoor sporting events allowed up to 4,000 people or at 50%
of venue’s capacity, whichever is lower. Large outdoor seated
venues, where crowds can be distributed, allowed up to 10,000
people or 25% of total seated capacity, whichever is lower
Step 1 of BC’s Restart Plan (13):
• Increased attendance allowed at events such as weddings and
funerals (e.g., weddings allowed to have more than 30 guests
from June 21st)
• Physical distancing and masks continue to be required in
public indoor settings
Travel:
Personal gatherings:
• International travel to “green list” countries resumes
• Indoor gatherings of up to 5 people or 1 other household
Businesses:
• Outdoor gatherings of up to 10 people continue
• Indoor hospitality, entertainment venues, and hotels open
Organized gatherings:
Offices and workplaces:
• Indoor seated gatherings of up to 10 people*
• Continued recommendation to work from home if possible
• Outdoor seated gatherings (e.g., weddings) of up to 50 people*
Sports and exercise:
• Indoor or outdoor worship services of up to 50 people*
• Adult indoor group sports and exercise classes resume
Travel:
Step 4 postponed from June 21st until after the study period
due to rising Delta variant cases.
• Recreational travel within own travel zone
• Non-essential travel between the government’s three
designated travel zones still restricted
Businesses:
• Indoor and outdoor dining for groups up to 6 people, not
restricted to own household or core bubble
• Liquor served until 10pm
Offices and workplaces:
• Start of gradual return to workplaces
• Employers must continue to have a COVID-19 Safety Plan and
daily health check in place
Sports and exercise:
• Low-intensity indoor fitness classes (e.g., Pilates) resume with
limited capacity
• Outdoor team sports are allowed for all ages, without
spectators
Time period: June 15 to June 30, 2021
Step 2 of BC’s Restart Plan (14):
• Physical distancing and masks continue to be required in
public indoor settings.
Personal gatherings:
• Outdoor gatherings of up to 50 people (e.g., birthday parties,
backyard BBQs, block parties)
• Indoor gatherings of up to 5 people or 1 other household
Organized gatherings:
• Indoor seated gatherings of up to 50 people*
• Outdoor gatherings of up to 50 people*
• Indoor or outdoor worship services of up to 50 people*
Travel:
• Recreational travel within BC
Businesses:
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British Columbia (BC)
England
• Indoor and outdoor dining for groups up to 6 people, not
restricted to own household or core bubble
• Liquor served until midnight
• Banquet halls reopen with limited capacity*
Offices and workplaces:
• Continued return to workplaces
• Small, in-person meetings allowed
• Employers must continue to have a COVID-19 Safety Plan and
daily health check in place
Sports and exercise:
• Indoor high- and low-intensity group exercise allowed with
reduced capacity
• Indoor and outdoor team sports allowed for all ages
• Up to 50 spectators allowed outdoors, no spectators at any
indoor sport activities
*With an approved BC COVID-19 Safety Plan.
Appendix Table 2. Combined screening and detection strategy for variants of concern in British Columbia, Canada, March 1 to
June 30, 2021*
Dates
VOC detection strategy
March 1 to May 29, 2021
Combined VOC testing strategy using targeted VOC SNP qPCR (“screening”) and whole-genome
sequencing (WGS):
• Under the combined testing strategy, ≈80 to 99% of positive samples were screened for VOCs
each week; a subset of screened cases were further confirmed by WGS. See below for details on
screening methods and proportion of screened cases further confirmed by WGS, by time period.
• A separate subset of positive samples underwent WGS, including: a random sample for baseline
surveillance, those associated with clusters/outbreaks, hospitalization, re-infection, and vaccine
breakthrough, and those associated with international travelers arriving at the BC border.
March 1 to 31, 2021:
VOC SNP qPCR screening methods in BC primarily only detected the N501Y mutation (present in
Alpha, Beta, and Gamma VOCs). One hospital in BC implemented K417T mutation screening for
Gamma VOC detection from March 21, 2021 onwards. During this time period, all presumptive
positive SNP qPCR results were confirmed by WGS at the BCCDC PHL.
April 1 to May 29, 2021:
VOC SNP qPCR screening methods were modified to incorporate both N501Y and E484K
mutation screening at the BCCDC PHL (E484K mutation is detected in Beta and Gamma VOCs,
but rarely in Alpha VOC). Specimens that tested positive for N501Y alone were identified as
presumptive B.1.1.7 lineage; ~10% were confirmed by WGS. In addition, only ~25% of specimens
that tested positive for N501Y and another mutation were confirmed by WGS. Based on
epidemiology at the time, VOC screening results with both E484K and N501Y mutations were
assumed to be Gamma VOC, given the very low prevalence of Beta VOC in BC.
May 30 to June 30, 2021
All positive samples in BC had WGS attempted.
*BC, British Columbia; BCCDC PHL, British Columbia Centre for Disease Control Public Health Laboratory; SNP qPCR, single-nucleotide
polymorphism quantitative PCR; VOC, variant of concern; WGS, whole-genome sequencing.
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Appendix Figure 2. Comparison of England and British Columbia vaccination coverage (A) and
proportion of genotyped cases identified as Delta variant of concern (B). Vaccine dose coverage includes
the coverage of both dose one and dose two by age group, with the 80% coverage highlighted as a
dashed line for clarity. Population vaccination coverage data were extracted from the UK Government
COVID-19 dashboard (15) for England and from the Provincial Immunization Registry for BC. Note that
England had not started vaccination of the adolescent group (ages 12–17) before July 2021. Data for the
Delta variant in England was extracted from the UK Health Security Agency Technical Briefing 19 (16) of
all available genotyped cases. British Columbia Delta variant prevalence was extracted from all cases
genotyped through screening and background surveillance.
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Appendix Table 3. Case definitions for variants of concern*
VOC
Delta
Alpha
Gamma
Beta‡
*VOC, variant of concern.
†Screening employed targeted single-nucleotide polymorphism quantitative polymerase chain reaction (SNP qPCR).
‡Based on epidemiology at the time, VOC screening results with both E484K and N501Y mutations were assumed to be Gamma VOC, given the
very low prevalence of Beta VOC in BC.
Appendix Table 4. Modeling approach and parameters used for each counterfactual scenario
Scenario
Modeling approach
Parameters and explanation
Baseline
Baseline transmission was fit using a Bayesian
approach to daily BC PCR-confirmed COVID-19
cases. Transmission was modeled as a piecewise
constant function with pre-specified breakpoints.
Breakpoints were selected based on changes in public
health measures or population behavior. The start dates
for each segment were: 2020–03–15, 2020–05–10,
2020–09–08, 2020–09–21, 2020–11–10, 2021–01–25,
2021–03–29, 2021–04–05, 2021–05–25.
Introduction of
Delta variant
Logistic growth curve multiplied by transmission
rate β to replicate the relative increase in
transmission as the Delta variant became dominant.
The parameters include the time of introduction and
the time to the proportion of Delta being 90%
among all variants.
The BC scenario ramp had a start date of 2021–05–25
and a time to dominance of 25 weeks. The England
scenario had a start date of 2021–05–01 and a time to
dominance of 4 weeks to reflect the differences in the
proportional change in Delta between both jurisdictions.
For each scenario, Delta increased transmission by 50%
(17).
Public health
measures and
health behavior
A further change in the transmission was included
to characterize the changes in public health
measures and behavior following their introduction
on 2021–04–05 in BC. This was modeled as a step-
change in the transmission term after
implementation of the measures.
In the BC scenario, the transmission term was fitted to
historical data and so no further changes needed to be
included. For the England scenario, the transmission
term is multiplied by a factor of 50% reflecting no
changes in public health measures following 2021–04–
05.
Vaccination roll-
out and coverage
The exact proportion of vaccination by age group
were extracted for both BC and England
jurisdictions. For each vaccination coverage, an
estimate of BC’s population structure and contact
rates by age group were used to derive an age-
adjusted vaccination rate for each scenario.
Proportion of each age group vaccinated based on data
for BC and England. Number of weekly contacts per age
group based on BC-Mix survey data (18) were:
<2 y: 6, 2–5 y: 12, 6–17 y: 13, 18–24 y: 44, 25–34 y: 44,
35–44 y: 48, 45–54 y: 48, 55–64 y: 24, 65–74 y: 21, >75
y: 17.
Vaccination
product
The vaccine transmission-blocking effectiveness
was selected for each scenario based on the
dominant vaccine product for each jurisdiction
during the study period. In BC this was BNT162b2
and in England this was ChAdOX1.
Vaccine effectiveness for the BC scenario was 71.8%
after one dose and 89% after two doses. Vaccine
effectiveness for the England scenario was 58% after
one dose and 77% after two doses.
*BC, British Columbia.
Appendix Table 5. Transmission-blocking efficacy parameters used in counterfactual modeling by vaccine product and first and
second dose
Vaccine product
Dose one
Dose two
BNT162b2 (Pfizer)
71.8%
89%
ChAdOx1 (AstraZeneca)
58%
77%
*Efficacy parameters for vaccination incorporated both a reduction in the
probability of incidence infection as well as reduction in onward
transmission if infected while vaccinated. Estimates for vaccine
transmission-blocking efficacy and onward-transmission efficacy were
derived from values presented in the UK Scientific Pandemic Influenza
Group on Modeling, Operational subgroup (SPI-M-O) of the Scientific
Advisory Group for Emergencies (SAGE) July 7th modeling group report
(19) where a range of optimistic to more pessimistic vaccine assumptions
were provided by different modeling groups. The total transmission
blocking probability is 1-(1–0.6)*(1–0.45) = 0.78 under the optimistic
scenario and 1-(1–0.53)*(1–0.4) = 0.718 under the pessimistic scenario for
BNT162b2, rising to 0.89 under the second dose. For ChAdOx1, after one
dose, this is 0.58 under the pessimistic and 0.65 under the optimistic
scenarios, rising to 0.77 under the second dose pessimistic and 0.8 under
the optimistic scenarios, respectively. Scenarios in British Columbia were
more in line with pessimistic assumptions for BNT162b2, so for ChAdOx1
we also selected the pessimistic assumption.
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Appendix Figure 3. Sample median number of contacts by age group in British Columbia, Canada,
February 28 to September 4, 2021. Reported contacts by age group in BC extracted from BC Mix COVID-
19 Survey data (18). Fitted lines constructed using local polynomial regression with LOESS method.
BC, British Columbia.
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Appendix Figure 4. COVID-19 cases in British Columbia, Canada by Delta variant of concern, other
lineage, or unknown lineage, with specimen collection date between March 1 and August 28, 2021,
overlaid with 12 year and older population COVID-19 vaccination coverage by dose received. Step 3 of
BC’s Restart Plan included lifting of the mask mandate in indoor public spaces, removal of limits on
indoor and outdoor personal gatherings, increased capacity for indoor and outdoor organized gatherings,
allowing of Canada-wide recreational travel, increased capacity at indoor sports and exercise facilities, re-
opening of casinos and nightclubs, and return to normal hours for liquor service at restaurants, bars and
pubs, with no group limits for tables (20) (Appendix Table 6). BC, British Columbia; VOC, variant of
concern.
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Appendix Table 6. Changes to public health and social measures in British Columbia, Canada following July 1, 2021 move to Step
3 of provincial Restart Plan
British Columbia
Implemented on July 1, 2021
Step 3 of BC’s Restart Plan (20):
• Masks recommended until fully vaccinated, but not mandatory, in public indoor spaces
• Physical distancing remains in place
Personal gatherings:
• No limits on personal gathering sizes indoors or outdoors
Organized gatherings:
• Indoor organized gatherings of up to 50 people, or 50% capacity, allowed with a COVID-19 Safety Plan
• Outdoor organized gatherings of up to 5,000 people, or 50% capacity, allowed with a COVID-19 Safety Plan
• Fairs, festivals, and trade shows return to normal, with Communicable Disease Plan in place
Travel:
• Recreational travel within Canada allowed
Businesses, offices, and workplaces:
• No limits on group sizes for indoor or outdoor dining
• Return to regular liquor service
• Bingo halls, casinos, and nightclubs reopen with reduced capacity
• Seminars and bigger meetings allowed for offices and workplaces
Sports and exercise:
• Return to normal for sports and exercise facilities, with Communicable Disease Plan in place
While BC’s state of public health emergency remained in effect to support amended public health orders from the provincial health
officer, Step 3 of BC’s Restart Plan also signaled the end of BC’s provincial state of emergency in response to the COVID-19
pandemic, which had been in place since March 2020 (20). The provincial state of emergency had granted the BC government
additional powers such as the ability to enforce the mandatory mask policy and travel restrictions that had been in place.
*BC, British Columbia.
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